Very low frequencies are difficult to contain in a typical living space and typical construction. You may ask some pros how to handle this situation.

As to the rubber feet and granite, if the subwoofer cone moves up and down, it could excite the granite/rubber combination depending on how stiff the rubber disks are. In my own case, a driver moving up/down worked best for cleaner bass if the box is coupled to the floor through spike feet, not rubber or carpet.

Graham J Samuels wrote:

Thanks for the reply , Yes proly right about the spikes. I took the rubber feet off the sub and replaced them with the oem spikes , Now the sub has a more developed response not in your face but in a suttle way I can tell there is a change. As far as the rubber feet under the granite, Well I did not want to cause any damage to my floor this was the reason. In the future I may try to spike the slab as well but that will involve fitting the spikes to the slab and then decouple them with disks, Maybe I can use some sort of iso nods or cones to do this. And best off all still no complaints.

It sound like your problem has opposing goals. If you want to eliminate structural vibration of shaking floors and disturbing neighbors due to the vibration, then you need to isolate the subwoofer from the floor. The right type of rubber floor and granite slabs might help. Without actual numbers, one can't determine if this reduces vibration transmission to the floor or increases it.

If you have spikes coupling the sub to the granite and the rubber feet beneath the granite slab to the floor, the effect is increasing the subwoofer cabinet mass with the granite, but putting a rubber spring coupling the entire sub-granite system to the floor. Since subwoofers are not exactly light in weight, and added granite to the mass of the sub cabinet, the rubber feet below the granite probably must be fairly stiff, perhaps vibrating at frequencies above the subwoofer rolloff. Again, without actual numbers, I'm just guessing here based upon ballpark estimates.

If you want to get better sonics, then the idea of spikes coupling the subwoofer to the floor makes the subwoofer cabinet more 'attached' to the floor. This makes the cabinet act like it has gained additional mass (the floor) and may vibrate less in the vertical direction (assuming the subwoofer driver moves in the same direction). This makes the driver move the air and less moving a shaky cabinet on a resiliant foundation (carpet for example).

On other thing to try is to use the spikes on the floor, and put the granite on top of the subwoofer. Spikes couple the sub to the floor to act like more mass for the sub cabinet, and the granite on top adds more mass as well as push the spikes harder so it's less easy for the sub to vibrate the cabinet if driven very hard.